The art is replete with various types of anti-theft devices for preventing unauthorized use or theft of vehicles. Some of these devices are relatively simple and are calculated to stop or discourage the unskilled thief but are relatively ineffective in deterring the professional thief. More sophisticated anti-theft devices have been proposed which are relatively complex and may employ complex electronic circuits, typically employing a microcomputer. These latter-mentioned devices, however are relatively expensive in terms of their components and the labor required to assemble them and are subject to reliability problems. Some of these devices impose relatively large idle-current demands on the automotive electrical system and others, in spite of their relative complexity, are not completely effective in deterring the professional thief.
It is generally thought that an anti-theft device which deters the thief for at least five minutes provides an effective anti-theft system. In order to accomplish this objective, the system must be: (1) relatively inaccessible, (2) not readily bypassed or deactivated, and (3) if employing a code, the code must not be readily decipherable either by multiple trial-and-error attempts or by electrical measurements. Moreover, such a device should not interfere with the normal operation of the vehicle.